A pentanuclear dysprosium hydroxy cluster of composition [Dy 5(mu 4-OH)(mu 3-OH) 4(mu-eta (2)-Ph 2acac) 4(eta (2)-Ph 2acac) 6] ( 1; Ph 2acac = dibenzoylmethanide) was prepared starting from [DyCl 3.6H 2O] and dibenzoylmethane. Both static (dc) and dynamic (ac) magnetic properties of 1 have been studied. Below 3 K, the appearance of slow relaxation of the magnetization typical for single-molecule magnets is seen, even if no hysteresis effects on the M vs H data are observed above 1.8 K.

The Schiff base compound 2,2'-{[(2-aminoethyl)imino]bis[2,1-ethanediyl-nitriloethylidyne]}bis-2-hydroxy-benzoic acid (H(4)L) as a proligand was prepared in situ. This proligand has three potential coordination pockets which make it possible to accommodate from one to three metal ions allowing for the possible formation of mono-, di-, and trinuclear complexes. Reaction of in situ prepared H(4)L with Dy(NO(3))(3)·5H(2)O resulted in the formation of a mononuclear complex [Dy(H(3)L)(2)](NO(3))·(EtOH)·8(H(2)O) (1), which shows SMM behavior. In contrast, reaction of in situ prepared H(4)L with Mn(ClO(4))(2)·6H(2)O and Dy(NO(3))(3)·5H(2)O in the presence of a base resulted in a trinuclear mixed 3d-4f complex (NHEt(3))(2)[Dy{Mn(L)}(2)](ClO(4))·2(H(2)O) (2). At low temperatures, compound 2 is a weak ferromagnet. Thus, the SMM behavior of compound 1 can be switched off by incorporating two Mn(II) ions in close proximity either side of the Dy(III). This quenching behavior is ascribed to the presence of the weak ferromagnetic interactions between the Mn(II) and Dy(III) ions, which at T > 2 K act as a fluctuating field causing the reversal of magnetization on the dysprosium ion. Mass spectrometric ion signals related to compounds 1 and 2 were both detected in positive and negative ion modes via electrospray ionization mass spectrometry. Hydrogen/deuterium exchange (HDX) reactions with ND(3) were performed in a FT-ICR Penning-trap mass spectrometer.

The reaction of CH 2 (PPh 2 NSiMe 3 ) 2 with n-butyllithium or potassium hydride in THF leads, after the recrystallization from toluene or n-heptane/diglyme, to the corresponding alkali derivatives [Li(THF)][CH(PPh 2 NSiMe 3 ) 2 ] (1), K[CH(PPh 2 NSiMe 3 ) 2 ] (2), and [K(digylme)][CH-(PPh 2 NSiMe 3 ) 2 ] (3). Upon coordination to the metal center the ligand forms a six membered metallacycle in which both phosphinimine nitrogen atoms bind to the metal atom.

The reaction of benzamidinato silicon trichloride [{PhC(NR)2}SiCl3] [R = Bu(t) (1), SiMe3 (2)] with 2 equiv of potassium in THF afforded mononuclear chlorosilylene [{PhC(NBu(t))2}SiCl] (3) and [{PhC(NSiMe3)2}2SiCl2] (4), respectively. Compound 4 was formed by the disproportionation of unstable [{PhC(NSiMe3)2}SiCl]. The reaction of [{PhC(NBu(t))2}SiCl3] (1) with 1 equiv of LiR (R = NMe2, OBu(t), OPr(i), PPr(i)2) in THF yielded [{PhC(NBu(t))2}SiCl2R] [R = NMe2 (5), OBu(t) (6), OPr(i) (7), PPr(i)2 (8)]. Treatment of 5-8 with 2 equiv of potassium in THF resulted in the novel heteroleptic silylene [{PhC(NBu(t))2}SiR] [R = NMe2 (9), OBu(t) (10), OPr(i) (11), PPr(i)2 (12)]. Compounds 4, 9, and 12 have been analyzed by X-ray crystallography.

[{(eta(5)-C(5)Me(5))(2)Sm}(4)P(8)], a molecular polyphosphide of the rare-earth elements having a realgar core structure, was synthesized by a one-electron redox reaction of divalent samarocen and white phosphorus.

Reaction of K{CH(PPh 2 NSiMe 3 ) 2 } (1) with anhydrous yttrium or lanthanide trichlorides leads to [{CH(PPh 2 NSiMe 3 ) 2 }LnCl 2 ] 2 (Ln ) Y (2a), Sm (2b), Er (2c), Dy (2d), Yb (2e), Lu (2f)). The single-crystal X-ray structures of these complexes show that the methine carbon is bound to the lanthanide atom. This is supported by DFT calculations, which show a comparable interaction. Due to the similar ion radii of the lanthanides, the single-crystal X-ray structures of 2a-f are isostructural. Further reaction of 2 with KNPh 2 afforded [{CH(PPh 2 NSiMe 3 ) 2 }Ln(NPh 2 ) 2 ] (Ln ) Y (3a), Sm (3b)). These complexes show in comparison to 2 a similar coordination behavior of the {CH(PPh 2 NSiMe 3 ) 2 }ligand in the solid state and in solution.

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Metal-metal bonds are of fundamental interest in many areas in natural science.[1] In the coordination chemistry of transition metals, single and multiple metal-metal bonds have[*] Dr.